The Application of Halogen-free Intumescent Flame Retardant in Polyolefin Zhu Feng Hangzhou JLS Flame Retardants Chemical Co., Ltd. Shen Kang Beijing ADD-TECH Consulting Co., Ltd. Abstract Halogen-free intumescent flame retardant is a kind of flame retardants with a quick development in recent years. However, in practice, we found a lot of problems which limited the use of such flame retardants in polyolefin. Research showed that different processing technology and additives have obvious influence to the flame retardancy and other properties of the material. Meanwhile, polyolefin have many different types and grades, like PP and PE. Different type and even different grade has different requirement for the flame retardant. This paper mainly studied the processing method of polyolefin with the halogen-free intumescent flame retardant, the related additives and the influence of the grades of polyolefin to the final flame retardancy of the material. Key Words： Halogen-free, Intumescent, Flame Retarded, Polyolefin, Additive

1. Background Over the past 10 years, halogen-free intumescent flame retardant (IFR) technology had been one of the important development trends in the flame retardants region. Many papers and researches studied on how to manufacture and use halogen-free flame retardants in polyolefin and other polymers. Some suppliers have manufactured a series of halogen-free intumescent flame retardants at smaller industrial scale. For example, there are Exolit AP750, AP760 of Clariant, Budit 3076 of Budeheim and PNP1 series of JLS. The mechanism of such systems is same. Though the acid donor, carbon donor and gas donor of the flame retardant system work together and form intumescent isolating carbon shell(char), it prevents the molten polymer from getting in tough with oxygen, heat and combustible gases1. In practice, we found that successful example in a large scale application of such IFR system is very few because of the peculiarity of such halogen-free intumescent flame retardants. For a successful halogen-free intumescent flame retardant polyolefin compound, it needs so many additives to work together besides the flame retardant, include dispersant, lubricant, modifier, antioxidant and etc. Such additives sometime caused problem to IFR system. It is possible that a few amount of such additives change the char forming processing and, they could bring the fateful influence to flame retardancy. On the other hand there is water-proof limitation commonly for such systems. We can modify the water-proof property, but any modification also could bring influence to flame retardancy. In addition, we must pay attention to the dispersion and extrusion processing.

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Because of all these problems, it was difficult to get stable and perfect flame retardancy when we use IFR.

2. Flame Retardant Mechanism of halogen-free intumescent flame retardant Based on P-N system, JLS-PNP1 series flame retardant is a high efficient halogen-free, intumescent, low smoke, non toxic and environmental friendly flame retardant. In fire, the acid donor, carbon donor and gas donor work together to form intumescent isolating carbon shell, which prevents the molten polymer from getting in tough with oxygen, heat and combustible gases. The flame retarded mechanism is taken place in the solid phase. Fig1 shows the mechanism. Acid donor

Flame resistance

Dehydration Carbon

Carbon donor

Intumescent carbon Shell

Catalyze to carbon Gas donor

Noncombustible gases

Fig1: Flame retardant mechanism of JLS-PNP1series

In this paper, we take JLS-PNP1C of JLS-PNP1 series as an example. In Fig2, intumescent flame retarded system makes the material self-extinguish when the cable leaves the fire and hinders after-glow effectively. It makes the cable to pass VW-1 test (single vertical burning) easily. At the beginning of fire, the IFR system starts dehydrating and decomposing to give out a lot of noncombustible gas, help molten polymer forming char to reduce combustible gas. While the fire is going along, it is forming the intumescent char shell. The char shell is strong and with excellent heat insulation. It owes to the thickness and lacunose structure with close skin of the char shell2.

Fig 2: The intumescent char forming procedure of PE with JLS-PNP1C

3. Surface Treatment - Flame Retardancy

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3.1. The influence of coupling agents treatment There are a lot of polar groups on the surface of halogen-free intumescent flame retardant, for example -NH2, -OH and etc, but polyolefin is no polar, the flame retardants should be treated by coupling agent to ensure disperse. Normally we can use silane coupling agent, titanate coupling agent and fatty acid, see Table 1. Table 1： Flame Retardancy -Coupling agents Treatment （Based on 100phr PP+ 38phrJLS-PNP1， LOI=30）

Addition

Silane coupling agent （KH550） 30 32 33 32 Smooth

Titanate coupling agent （KR-138） 30 31 33 33 Smooth, little yellow

28 26 24 24 Disperse badly

1.86

2.23

12.00

1

0．2% 0．5% 1．0% 2．0% Surface Weigh Loss at water2, %

Stearic Acid

1. Addition: Based on flame retardant. After treating flame retardants, add flame retardants in the compound 2.Dip method: Based on 1% addition， the sample withδ=1mm and120X120mm plate dip in water (70℃X168 hours). Weigh Loss ratio base on the total weigh of the sample plate. If used no treatment flame retardants, Weigh Loss= 2.1%。

In Table 1, we find that for stearic acid(SA), it makes IFR difficult to disperse in PP, which makes the flame retardancy very bad. The reason is probably that –COOH of SA can react with -NH2 of IFR and then to cause IFR powder agglomeration. SA also changes carbon structure too much to form the tight carbon armor. Silane coupling agent and titanate coupling agent can make the IFR to disperse easily, KR-138 contain of pyrophosphoric ester which it is no influence to flame retardant. However, at 210 ℃ ， the compound contain of titanate coupling agent and IFR becomes instable, we find it a little yellow. Also there is negative influence to flame retardancy when the addition of silane coupling agent is above 2%. In fire silane coupling agent changes to SiO2 which increases the specific gravity of intumescent foam to reduce expandable ratio. In the paper we treat IFR with thermoset resin to modify the flame retardants water-proof. Thermoset resin contain of silicon resin, epoxy resin, MF resin and so on, which make IFR more dispersive and better water-proof, of course there is somewhat negative influence to flame retardancy. When surface coated, the IFR could not contact polymer straightly before the coating resin breaks up, see Fig3. Coating armor

In fire Coating armor BREAK UP JLS-PNP1

JLS-PNP1

Table 2： Thermoset Resin treatment - Flame Retardancy (Based on 100phr PE + 55 phrJLS-PNP1， LOI=35)

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Item 2% 5% Weigh Loss at water，%

Silicon resin 32 30 0.61

Epoxy resin 33 32 1.02

MF 30 27 0.03

No treatment LOI=35 4.12

1．Base on 5%wt resin treatment

In Table 2, there is negative influence to flame retardancy enormously. The influence of MF resin is the biggest. For epoxy resin, it is smaller. The reason is that epoxy is oxygen polymer, which can advance IFR to form the intumescent carbon shell. At the same time we found that IFR decreased the heat stability of the epoxy resin. At 200℃, the compound is becoming yellow.

3.2. The influence of particle size of IFR IFR is solid powder, whose particle size brings some influence to flame retardancy. In PE, 15-20μm particle size is better than 8-12μm at flame retardancy and tensile strength. The bigger the surface area of the finer particle size powders makes them more difficult to disperse and then reduces the tensile strength by 11%. We treat it by coupling agent to improve dispersion in polyolefin. An example of PE compound is showed in Table 3. Table 3：The Particle size of IFR - Flame retardancy (Based on 100phr PE + 52 phr JLS-PNP1)

Average diameter μm

8-12

LOI Weigh Loss at water，% Tensile，Mpa

31 4.6 15

15-20 30 2.1 17

20-25 29 2.1 14

8-12 (1% silane coupling agent treatment) 32 1.9 19

4. How Additives Impact Flame Retardancy In this paper we find that ordinary additives bring some influence to IFR, for example filler, lubricant and so on.

4.1. The influence of different fillers We often add fillers in plastics. In brominated flame retardants system, we must add fillers (for example Talcum) as synergists to attain no dipping. How do the fillers affect the IFR, see Table 4.

Item

CaCO3

2% 5% 10%

32 27